Lecture 1 - Skeletal development Flashcards
What is the diaphysis?
The diaphysis is the central shaft of the bone made up of:
- cortical bone
- bone marrow (red and yellow)
- adipose tissue
What is the Epiphysis?
The rounded end of the long bone:
- joint with adjacent bone covered with articular cartilage
- filled with red bone marrow (produces RBC)
What is the Metaphysis?
Wide portion of the long bone between epiphysis and diaphysis:
- contains growth plate
Mesenchyme
Embryonic tissue which develops into connective and skeletal tissues (incl. blood and lymph)
Three stages of joint formation
Interzone appearance:
- tri-laminar structure
- two cartilaginous outer layers separated by intermediate later (flattened mesenchymal cells)
Morphogenesis:
- beginning of the shape
- prenatal movements important
Cavitation:
- physical separation of rudiments
- mechanical forces essential
Intramembranous ossification
Direct mineralisation:
MSCs (mesenchymal stem cells) differentiate into osteoblasts - secrete osteoid matrix
Forms most of compact bone (ribs, skull)
Endochondral ossification
Cartilage replaced by mineralised tissue:
- Chondrocytes enlarge and secrete cells for mineral deposition
- calcification of matrix
- apoptosis of chondrocytes
- blood vessels invade and bring hematopoietic and osteoprogenitor cells
- osteoblasts use calcified matrix as a scaffold and secrete osteoid to form bone
Forms most of future cancellous bone - vertebral column, sternum
Where are the primary and secondary centres of ossification?
Primary centre = first area of bone to ossify (e.g. diaphysis)
Secondary centre = appears after primary centre has already appeared (e.g. epiphyses)
Long bone development
- bone collar forms around hyaline cartilage
- cavitation of cartilage
- invasion of internal cavities
- formation of the medullary cavity
- secondary ossification centres in epiphyses (we do not want the skeleton to break during birth so we need to make sure its strong enough to withstand the birthing process)
- hyaline cartilage remains only in epiphyseal plates
Skeletal growth prenatally and postnatally
Prenatally: longitudinal growth at the diaphyseal growth plates
Postnatally: epiphyseal and diaphyseal growth
What happens when we stop growing?
Diaphyseal and epiphyseal centres of ossification meet. Growth plate is replaced by epiphyseal line
Achondroplasia
Mutation in FGFR3 gene. Growth plate fuses early and can’t grow anymore
- limits progress of ossification
- common cause of dwarfism
DDH Risk factors
- female
- family history
- ligament laxity
- breech
- lack of in utero fluid
- left hip
- large baby
- first born
- tight swaddling after birth
What is a Cartilage Growth Plate?
Growth plates are found in immature bones and are the driver behind longitudinal growth of a bone. They have a specific morphology with a zonal arrangement of chondrocytes composed of resting, proliferating and hypertrophic chondrocytes, and a zone of calcified
cartilage/ossification. In long bones there are two types of growth plates: diaphyseal (primary ossification centre) and epiphyseal (secondary ossification centres). Prenatally growth is due
primarily to growth at the diaphyseal plate and postnatally growth is due to both epiphyseal and diaphyseal plates. Growth stops when the diaphyseal and epiphyseal plates meet to form the epiphyseal line.
Muscleless limb Mice can aid the study of aspects of skeletal development
- Ossification initiation
- ossification progression
- bone proportion
- joint formation
- joint shape
- effect of passive movements
- genetic influences
This is because a lack of skeletal muscle means the forces on the bones and joints are lower than usual. By comparing the results from muscleless limb mice with those of ‘normal’ mice it can be determined which aspects of skeletal development are driven by genetic or biochemical
factors, rather than biomechanics.
